Using the same study cohort as the Genetics of Atherosclerosis in Mexican Americans study, this protocol has as its objective the identification and characterization of the genetic determinants of low bone density. Since the cohort has already had extensive interviews on a wide range of lifestyle and medical variables, there is a base from which to perform further study. The individuals will be re-examined and bone density will be measured at three sites by dual photon absorptiometry (DEXA). Additional biochemical markers of bone density-related phenotypes will also be obtained.